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median between matrix column

6 messages · arun, Jessica Streicher, Eliza Botto

arun
# 
HI,
May be this helps you (if I understand it correctly):
set.seed(1)
mat1<-matrix(sample(1:500,160,replace=TRUE),ncol=16)
?res<-do.call(rbind,lapply(1:ncol(mat1[,-16]),function(i) median(sort(stack(as.data.frame(mat1[,c(i,16)]))[,1]))))
?res
#?????? [,1]
?#[1,] 239.0
?#[2,] 238.0
?#[3,] 181.5
?#[4,] 244.5
?#[5,] 265.0
?#[6,] 212.0
?#[7,] 228.5
?#[8,] 233.0
?#[9,] 182.5
#[10,] 239.5
#[11,] 233.5
#[12,] 220.0
#[13,] 235.0
#[14,] 259.0
#[15,] 227.0

A.K.





----- Original Message -----
From: eliza botto <eliza_botto at hotmail.com>
To: "r-help at r-project.org" <r-help at r-project.org>
Cc: 
Sent: Monday, October 15, 2012 8:20 AM
Subject: [R] median between matrix column


Dear useRs,

1.? ? how to calculate single median value for two columns of a matrix?
2.? ? i have a matrix of 16 columns and 365 rows, how to calculate median between columns 1 and 16, 2 and 16, 3 and 16, 4 and 16, 5 and 16 till 15th column. is there a loop command to do the said operation?

regards
eliza? ??? ???  ??? ?  ??? ??? ? 
??? [[alternative HTML version deleted]]

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and provide commented, minimal, self-contained, reproducible code.
Jessica Streicher
# 
m<-matrix(1:10,ncol=5)
[,1] [,2] [,3] [,4] [,5]
[1,]    1    3    5    7    9
[2,]    2    4    6    8   10

apply(m,2,function(x){median(x,m[,5])})
[1] 5.5 6.5 7.5 8.5 9.5

Though i am not 100% sure thats what you mean. But the median of each row between two columns kind of doesn't make much sense to me, its only 2 values then after all.
On 15.10.2012, at 14:20, eliza botto wrote:

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        
      

    

    

      
      

        


  

        

      Jessica Streicher
    

    

      
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Actually i just saw that i copied the wrong code

apply(m,2,function(x){median(c(x,m[,5]))})

it should be.

Sorry if this confused anyone.

        
On 15.10.2012, at 15:32, eliza botto wrote:

        

            

      
      
      
    

        

      
      
    

            

      
      
      
    

        

      
      
    

  
  


  


      

    

    

      
      

        


  

        

      arun
    

    

      
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Dear Eliza,

No problem.

In my solution, you can delete the sort() and get the same result.
?res1<-do.call(rbind,lapply(1:ncol(mat1[,-16]),function(i) median(stack(as.data.frame(mat1[,c(i,16)]))[,1])))
head(res1)
?# ??? [,1]
#[1,] 239.0
#[2,] 238.0
#[3,] 181.5
#[4,] 244.5
#[5,] 265.0
#[6,] 212.0
A.K.